FR2524356A1 - PROCESS AND DEVICE FOR THE MANUFACTURE OF HIGH PURITY METAL POWDERS WITHOUT CERAMIC MATERIALS - Google Patents

Abstract

THE INVENTION CONCERNS A PROCESS FOR MANUFACTURING METAL POWDERS FREE OF CERAMIC MATERIALS, WHICH OPERATES BY SPRAYING A MELT MASS FLOWING FREELY FROM A CRUCIBLE BY MEANS OF A GAS CURRENT AND BY CONSECUTIVE SOLIDIFICATION. TO RESOLVE THIS PROBLEM, AND TO BE ABLE TO PRODUCE IN DEPTH OF A LARGE QUANTITY OF MELT MASSED POWDERS WHICH ARE FREE OF CERAMIC PARTICLES, IT IS PROPOSED ACCORDING TO THE INVENTION TO PRODUCE AND MAINTAIN A MELT MASS AT LEAST 16 IN A CRUCIBLE OF AN ARC 15 ELECTRODE, TO PRODUCE A SOLIDIFIED METAL LAYER IN THE CRUCIBLE THANKS TO A THERMAL BALANCE OF THIS CRUCIBLE, AND TO LET THE MELT MASS FROM ABOVE A SPOUT 18 CARRIED BY THE CRUCIBLE AND SPRAY IT BELOW FROM THE SPILL.

Description

The invention relates to a method of manufacturing

  high purity metallic powders without

  ceramics, which operates by spraying a melt which flows freely from a crucible or melting vessel, by means of a gaseous stream, and by solidifying

consecutively.

  Processes of the kind mentioned at the beginning are frequently

  also referred to as the atomization process of

  In the state of the art, the mass is conveyed

  melted from a ceramic-coated induction furnace to the spraying device via a

  casting funnel which is in most cases equal to

  In this process, both the coating and the

  of the induction furnace than the ceramic funnel

  ceramics can determine a contamination of the

  formed by ceramic particles and thereby

  considerably impair the quality of the powder

  Metallic. Therefore, for the manufacture of a metal powder devoid of ceramic materials, it has been used up to now for the division of the molten metal mass centrifugal process In this process, it is used

  raw material ingots which have been

  their proportion of ceramic by reflow in a vacuum arc furnace, in an electron beam melting furnace or in a slag remelting plant

  The ingots considered were once again

  and the molten mass dripping or

  flowing through a channel was conducted to a centrifuge tray on which the melt was divided

  in very fine droplets under the action of central forces

  trifuge (German Offenlegungsschrift No. 25 28 999).

  Although, with such a process, one can manufacture a high purity metal powder, one runs into

  practical disadvantage of low specific productivity.

  of the device, coupled with a relatively broad particle spectrum, compared to atomization by

gas.

  It is also already known to use an ingot as a fuse electrode and to burst between this electrode and a rotating drum cooled by water

  an arc that melts the ingot However, in this

  also yielded a broad spectrum of particle size

  and the specific productivity of the device is ex-

very weak.

  The combination of the electron beam melting process and the metal atomization process

  no good results because, in the case of atomic

  metal, it is not possible to produce a sufficiently high vacuum with a bearable

  -15 because of the continuous introduction of the spraying gas

  while the electron beams require

  their spread a vacuum as good as possible.

  In addition, the combination of the atomization process

  metals and the plasma smelting process

  unusable because, because of

  vorable and energy balance also unfavorable, it was necessary to install fusion powers

  to plasma of an unacceptable value from the point of view of

nomic.

  The purpose of the invention is therefore to indicate a

  assigned in the beginning in which, despite the use of a spraying process, and the large amount of melt conveyed per unit of

  time that is necessary for this process, we can

  powders which are free of ceramic particles

c.

  According to the invention, the solution of the problem posed

  in that the melt is produced and maintained in a crucible by means of an arc electrode, in a manner known in the art, by adjusting the balance

  of the crucible, the latter produces a

  solidified metal and in that the

  melt over a weir provided on the crucible

  set and spray below the spillway.

  Unlike electron beam fusion, fusion by means of an arc electrode can also be performed under atmospheric pressure so

  that the merger process is not disrupted by the

  troduction of considerable amounts of pulverulent gas.

  thanks to the production of a metallic layer

  solidified on the inner wall of the crucible, it avoids

  ficament the effect of exchange between the melt and the crucible The layer of solidified metal is frequently called "skull" (also known under the name of "skull") It is certainly already known in principle a fusion process of this kind but so far this process has been used exclusively for the manufacture of

  Precision vacuum casting parts.

  The thickness of the solidified metal layer depends

  of the thermal balance of the crucible, that is to say, the quantity

  heat brought by the process of the bow, from a

  part of the quantity of heat discharged through the

  the cooling fluid, on the other hand It is therefore possible, by adjusting the amounts of heat

  respectively brought and evacuated, to act on the thick-

  of the solidified metal layer.

  A feature of essential importance

  in that the melt flows over a drain

  in the evening, that is above the highest point of the melt bath, without having previously been in contact with the crucible metal, and then sprayed below the spillway. wide limits the amount of heat brought in, which also determines the melting speed so that

  the process according to the invention can in any case

  the fusion power needed to achieve

  high production capacity The atomization of the metal re-

  a process by which it is possible to achieve high speeds of spraying.

  process, a large range of variation can be obtained.

  with regard to the particle size spectrum Se-

  In the process parameters, the particle size spectrum may be narrower or wider; otherwise,

  it is possible to shift the maximum of the spectrum of

  In addition to this, the cooling properties

  However, the invention consists of a combination of the "skull" melting process (known as the "process") of the metal atomization, which results in extremely rapid cooling of the melt. 'tkull-melting'), and the process

atomization of the metal.

  According to another characteristic of the invention, it is particularly advantageous to heat the weir of the

  crucible with power control by means of a

  This measurement affects two characteristic quantities of the melt, namely the viscosity and the surface tension. By a weaker or stronger heating, the mass can be retained. in merging or accelerating the flow This naturally supposes that the molten metal arrives in a sufficient quantity, which can in turn be influenced

  by setting the arc heater However, independently

  of this, the amount of melt in the

  the crucible represents a certain buffer volume

  that, above the highest point of the weir, a kind of meniscus is formed, the size of which depends on the surface tension. If, now, the weir is heated more intensively, this equilibrium is influenced in the desired manner, namely , in the sense that flows a

  greater amount of melt per unit of time.

  In addition, the spillway is kept free of

  any melt being solidified.

  The invention also relates to a device for

  The implementation of the method according to the invention

  is composed of a melting chamber and spraying

  equipped with a crucible, a heating device> a spray nozzle, as well as a

  cooling and a powder collecting container.

  To solve the same problem and according to another characteristic of the invention, the crucible is constituted

  by a liquid-cooled crucible with

  evening, the heater is an arc electrode disposed above the crucible and the spray nozzle

  is arranged below the weir.

  As arc electrode we can consider as well

  permanent electrodes (graphite electrodes, electro-

  metal trodes cooled by water) or else

  what are called fusible electrodes which are

  composed of the same metal as the metal powder produced

by the process.

  According to another, very advantageous characteristic of the invention, such a device is characterized in that the melting and spraying chamber has, in its lower part, a lateral extension which

  extends in the direction of the spillway and encloses the

  does cooling and in that at the end of this

  extension, is arranged a collecting container of

dre.

  Usually, closed arc furnaces, in-

  the melting operation is carried out under an inert gas,

  are usually ovens whose main axis is

  tends in the vertical direction The invention consists

  therefore essentially to ride on such an oven, the former

  voltage is mainly vertical, an extension that

  extends in a lateral direction, that is to say horizontally

  The cooling zone of the powder

  which solidifies relatively rapidly in

  because of the high gas pressure, also has this

the horizontal pace.

  In this cooling zone the particles of

  metal are dispersed in a substantially

  rinzontale but, however, with the look of a parable

  ballistic which has a very strong lateral component.

  This side component is important for fitness

  operation of the device according to the invention,

  that, thanks to this construction feature, it

  It is not necessary to increase the height of

  of the whole system Here, it is necessary to

  account of the fact that in atomization processes

  already known metal, in which an outgoing gas at large

  speed of an annular slot nozzle blows the

  metal particles substantially downwards, one must dis-

  ask of what is called a well which increases considerably

  the construction height of such a device.

  Other features and advantages of the invention

  to be better understood by reading the description

  following an example of implementation and referring to

in the annexed drawing.

  The device is composed of a melting and spraying chamber 1 which encloses a substantially cylindrical well 2 in its upper and central part. The chamber is composed of an upper part 3 and a lower part 4 which are joined by an assembly 5, to enable the loading As shown, the upper part and the lower part of the chamber are made of double wall

  and provided with pipes 6 and 7 for the arrival of refrigerant fluid

  manager and pipes, 8 and 9 respectively, starting the refrigerant The upper part 3 of the chamber is attached to a not shown gallows and can

  be released laterally by pivoting.

  Through the upper part of the chamber is engaged, by means of a sliding seal 10 an electrode bar 11 which is connected to a unit

  supply of power via a pipe 12 To the ex-

  lower end of the electrode bar 11 is fixed

  a clamping device 13 in which an elec-

  trode 14 is mounted by a connection for safety and removable form The electrode tip 14 is joined by welding

  to an electrode 15 which constitutes the fuse electrode.

  Below the electrode 15 is a crucible

  16 which is connected by a line 17 to the optic pole

  of the power supply device The crucible

  consists of a double-wall crucible to cool

  by liquid and which is provided with one side of a

  In the course of the melting process, an arc 18 is formed between the electrode 15 and the molten metal bath contained in the crucible 16, which arc maintains the molten bath at the end of the melting process. the liquid state and continually melting a new quantity of material from the electrode 15 As already described above, to act on the balance sheet

  heat of the crate 16, it is produced between the mass

  due and the inner wall of this crucible a layer of metal

  solidified tal which is called "skull" (skull).

  che (not shown in the drawing) prevents the mass

  due to come in contact with the crucible.

  The metal that flows up and down the spillway is now placed in front of a spray nozzle 19 which

  is connected to a source of pressurized gas that is not

  through the conduct 20 In the absence

  gas flow, the metal flowing over the

  moldboard 18 would flow just in front of the front face of the spray nozzle 19 However, under the effect of a supply of the spray nozzle 19 with an appropriate pressure, the metal current is divided

  in very fine droplets that are ejected in a di-

  mainly horizontal, towards the right (view

on the face).

  For this purpose, in the lower region of the part

  4 of the chamber is provided an extension la-

  21, connected to this lower part and whose

  double wall is connected to a cooling device

  and in which there is a cooling zone

  22 It can be seen that extension 21 extends practically

  in the direction of the weir 18 as well as in the direction of the flow of the gas leaving the spray nozzle 19 At the other end of the extension 21

  the lower boundary wall of this extension is reali-

  in the form of a funnel 23 to which a powder collecting container 25 connects via

of a powder lock 24.

  At the junction between the lower part 4 and the

  longitudinally 21, is arranged in the wall of the chamber

  a plasma torch 26 which is oriented towards the

  moldboard 18 so that weir can be heated

by the plasma flame 27.

  Of course, various modifications may be

  provided by those skilled in the art to the device which has just been described by way of non-limiting example without

depart from the scope of the invention.

Claims (4)

  1 Process for producing metal powders   high purity free of ceramic materials, which ope-   by spraying a melt that flows   melting of a crucible or melting vessel, by means of a gaseous stream, and by subsequent solidification, characterized in that the melt is produced and maintained in a crucible by means of an arc electrode,   in a manner known per se, in that, by adjusting the bi-   the heat of the crucible, a solidified metal layer is produced in the crucible and   the melt over a weir provided on the crucible   set and spray below the spillway.   Process according to Claim 1, characterized in   the weir is heated, with adjustment of the   by means of a plasma torch so that the   melt stream is maintained substantially As.   3 Device for implementing the method se-   1, consisting of a melting and spraying chamber, provided with a crucible, a heating device, a spray nozzle, a cooling zone and a powder collecting container. characterized in that the crucible (16) is constituted by   a liquid-cooled crucible equipped with a   evening (18), in that the heating device is an arc electrode (15) disposed above the crucible (16)   and that the spray nozzle (19) is disposed over under weir (18).   4 Device according to claim 3, characterized in that the melting chamber and spray (1) has in its lower part a lateral extension (21) extending in the extension of the weir (18) and encloses the cooling zone (22) and in that   the end of the extension is a receptacle powder reader (25).   Device according to Claim 3, characterized in that a plasma torch (26) is arranged in the melting and spraying chamber (1). towards the spillway (18).